Rate control is an integral component of modern video compression systems. A compressed bit stream satisfies specific bandwidth and delay constraints that are imposed by the transmission medium. These constraints can be satisfied through rate control. Rate control algorithms vary the number of bits allocated to each picture, color component, set of blocks, or individual blocks, so that encoder and decoder buffer overflows and underflows may be avoided, and the target bit rate may be achieved with high accuracy. A basic unit may be a collection of adjacent pictures (or frames). Bit rate and complexity statistics may vary greatly among splices.
An objective of a video compression system is high compression performance, e.g., to achieve the lowest possible distortion given a fixed target number of bits for the compressed bit stream or equivalently to send the minimum possible number of bits for a fixed distortion value. An example of distortion measurement is peak signal-to-noise ratio (PSNR). Video encoders produce a compressed bit stream such that when a compliant decoder mechanism (e.g., a hypothetical reference decoder) decodes the compressed bit stream, a reconstructed video sequence is generated that can be displayed and viewed at a receiver side. It should be appreciated that a storage or transmission medium can send such a compressed bit stream to a receiver to be decoded in a variety of transport modes. Each one of these transport modes can have different delay and bandwidth constraints. Streaming the same bitstream over a network that lacks bandwidth to support such a bit rate may affect performance.
A mechanism for generating compressed bit streams that satisfy the bandwidth and delay constraints is rate control. Rate control may minimize visual distortion, generate bits that fit the communication channel, and may deter decoder input buffer overflow or starvation (e.g., that may result in an underflow).
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.